The present invention relates to a display unit and, more particularly, to improvement in or relating to means for transferring data to a character memory or graphic memory.
In a display unit in which the content of a character memory or graphic memory, used as a picture memory, is cyclically read out therefrom by a scanning address from a CRT controller to provide a display, the content of the picture memory must be rewritten for changing the content of the display. For this rewrite it is customary in the prior art to generate a write cycle immediately after each read cycle of the picture memory by the CRT controller and to transfer data stored in a work RAM to the picture memory through a microprocessor or directly through utilization of a direct memory access (DMA) function. With such data transfer means, however, it is necessary to generate the write cycle by hardware, resulting in the defect of an increased number of parts forming the hardware. Further, the larger the screen becomes or the more resolution is raised, the shorter the write enable time becomes; therefore, when the amount of data to be transferred is large, the rewrite takes much time. Moreover, since the display is also provided during the rewrite operation, it is blurred, or it is not smoothly switched.